This application claims priority from Korean Patent Application No. 2002-64524, filed on Oct. 22, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a method for forming an insulating thin film in the manufacture of a variety of electronic devices, and more particularly, to a method for forming a metal oxide thin film using atomic layer deposition (ALD).
2. Description of the Related Art
Generally, insulating films for electronic devices have been formed using physical vapor deposition (PVD) or chemical vapor deposition (CVD). Recently, the application of atomic layer deposition (ALD) in forming such insulating films is gradually increasing. As is well known, rather than simultaneously supplying source gases into a reactor, ALD involves sequentially alternating pulses of different kinds of source gases to form a thin film. In particular, the source gases are supplied sequentially into a reactor at predetermined time intervals as pulses by timely opening and closing gas supply valves for the source gases positioned near the entrance of the reactor. In general, a purge gas is supplied following each pulsing source gases at a predetermined rate to remove the remaining, un-reacted gas from the reactor. More recently, plasma enhanced ALD has been suggested for film formation.
Various kinds of insulating films used in the semiconductor field and which can be formed by ALD include, for example, gate dielectrics having a very small thickness requirement, capacitor dielectric layers, and insulating oxide layers. The use of Al2O3, ZrO2, or HfO2 for gate dielectrics and Al2O3, Ta2O5, or (Ba, Sr)TiO3 for capacitor dielectric layers have been investigated more actively in conjunction with the application of ALD. As a result, it was found that an Al2O3 film having a very uniform thickness can be formed through accurate film thickness control using ALD (Journal of the Electrochemical Society, 149(6), pp. C306(2002)).
ALD has been applied in the display device field as well as in the semiconductor field. Research has been conducted on ALD for a large-sized, thin film display having good step coverage and easy thickness control requirements. For example, for an electroluminescence display (ELD) formed by sequentially depositing a phosphor layer and an insulating layer, ALD involving in situ sequential deposition of these layers within the same reactor is preferred. An Al2O3 or an aluminum titanium oxide (ATO) layer is mostly used for the insulating layer. An Al2O3 layer formed using ALD is known to be denser and more uniform in thickness as compared with that formed using PVD or CVD.
Although the insulating layer deposited by ALD has a higher density and more uniform thickness, its electrical insulating properties should be strong enough to resist a high field strength for use in ELDs. However, if the thickness of the insulating layer is increased to prevent a breakdown, the threshold voltage for electroluminescenece may increase. Therefore, what is needed in the ELD field is a method for forming an insulating layer having a large dielectric constant and a high breakdown voltage even with a small thickness.
The present invention provides a method for forming an insulating layer, and more particularly, a metal oxide layer having a large dielectric constant and a high breakdown voltage even with a small thickness.
According to an aspect of the present invention, there is provided a method for incorporating nitrogen atoms into a metal oxide thin film in situ using plasma based on conventional atomic layer deposition (ALD). In particular, the metal oxide thin film is formed on a substrate by supplying a metal source compound and oxygen gas into a reactor in a cyclic fashion with sequential alternating pulses of the metal source compound and the oxygen gas, wherein the oxygen gas is activated into plasma in synchronization of the pulsing thereof, and a nitrogen source gas is further sequentially pulsed into the reactor and activated into plasma over the substrate in synchronization with the pulsing thereof. In other words, the invention is directed to the formation of a metal oxide thin film containing a trace of nitrogen by plasma enhanced atomic layer deposition (PEALD).
Since the thin film formation method according to the present invention is based on ALD, the advantages of ALD, such as the ability to grow a dense, uniform thin film, are ensured. In addition, the use of plasma in the present invention further increases the density of the thin film and the growth rate. Furthermore, since a trace of nitrogen atoms can be incorporated in situ into the thin film being grown, the resulting thin film is provided with improved breakdown characteristics. The added nitrogen atoms improve the passivation properties for the incorporation of moist or impurities as well as the electrical properties.
In an embodiment of the present invention, a nitrogen-containing Al2O3 thin film may be formed. The nitrogen-containing Al2O3 thin film according to the present invention has a high dielectric constant and can be used as a dielectric film for gate dielectric or memory dielectric layers of next generation semiconductor devices. In addition, the nitrogen-containing Al2O3 thin film can be applied to a various kinds of electronic devices as passivation purposes in order to prevent the incorporation of moist or impurities. In addition, the nitrogen-containing Al2O3 thin film is very suitable to be used as an insulating layer that is deposited on or underneath the phosphor layer of an electroluminescence device.